Introduction
Multiple sclerosis (MS) is an acquired, inflammatory, demyelinating disease of the central nervous system (CNS). In MS, cells of the immune system invade and destroy myelin, the fatty material that insulates nerves in the brain and spinal cord; other CNS cells produce a hardened sclerotic lesion (plaque) around the multiple demyelinated sites. Neurologic findings suggest lesions in separate areas of the CNS that have occurred at different times.
Multiple sclerosis (MS) is the most common autoimmune disease involving the nervous system. In the United States approximately 400,000 individuals suffer from MS. The cause of the disease is unknown, but genetic factors are important. The concordance rate among monozygotic twins is 30%, a 10-fold increase over dizygotic twins or first-degree relatives. The higher incidence rate among monozygotic twins emphasizes the importance of genetic factors, but the discordance rate of 70% among identical twins illuminates the role of nongenetic factors on disease penetrance. Among genetic factors, HLA class II genes exert an influence, with HLA DR2 carrying a 4-fold relative risk for northern European caucasoids.
A typical presentation of MS involves an initial course, running for several years to more than a decade, manifest by episodes of relapse followed by remission. Relapses often follow an episode of a viral infection of the upper respiratory system or gastrointestinal tract. In about one half of MS cases the disease progresses to a more chronic phase. Clinical problems may include disturbances in visual acuity, sometimes culminating in blindness; double vision; motor disturbances affecting walking and use of the hands; incoordination; bowel and bladder incontinence; spasticity; and sensory disturbances including loss of touch, pain, and temperature and proprioception. The pathology of the disease lies entirely in the central nervous system and is characterized by a classic picture of inflammation surrounding venules and extending into the myelin sheath.
Immune responses to various components of the myelin sheath have been detected in MS patients, including myelin basic protein (MBP), proteolipid protein (PLP), transaldolase, and 2′,3′ cyclic nucleotide 3′phosphodiesterases (CNP), as well as two members of the immunoglobulin supergene family found in the myelin sheath, myelin oligodendroglial glycoprotein (MOG) and myelin-associated glycoprotein (MAG) (Steinman et al. (1995) Mol. Med. Today 1:79-83). In addition, some inducible heat shock proteins, including crystallin-B, can be detected in glial cells in MS lesions and can stimulate an immune response in MS patients.
In human MS patients the following myelin proteins and epitopes were identified as targets of the autoimmune T and B cell response. Antibody eluted from MS brain plaques recognized myelin basic protein (MBP) peptide 83-97 (Wucherpfennig et al., J Clin Invest 100:1114-1122, 1997). Another study found approximately 50% of MS patients having peripheral blood lymphocyte (PBL) T cell reactivity against myelin oligodendrocyte glycoprotein (MOG) (6-10% control), 20% reactive against MBP (8-12% control), 8% reactive against PLP (0% control), 0% reactive MAG (0% control). In this study 7 of 10 MOG reactive patients had T cell proliferative responses focused on one of 3 peptide epitopes, including MOG 1-22, MOG 34-56, MOG 64-96 (Kerlero de Rosbo et al., Eur J Immunol 27, 3059-69, 1997). T and B cell (brain lesion-eluted Ab) response focused on MBP 87-99 (Oksenberg et al., Nature 362, 68-70, 1993). In MBP 87-99, the amino acid motif HFFK is a dominant target of both the T and B cell response (Wucherpfennig et al., J Clin Invest 100, 1114-22, 1997). Another study observed lymphocyte reactivity against myelin-associated oligodendrocytic basic protein (MOBP), including residues MOBP 21-39 and MOBP 37-60 (Holz et al., J Immunol 164, 1103-9, 2000). Using immunogold conjugates of MOG and MBP peptides to stain MS and control brains both MBP and MOG peptides were recognized by MS plaque-bound Abs (Genain and Hauser, Methods 10, 420-34, 1996).
Neuropathological findings suggest that antibodies may play a role in lesion formation in some multiple sclerosis patients. (Storch et al. Ann. Neurol. 43: 465-71, 1998). Autoantibodies recognizing several myelin proteins including MBP (Sellebjerg et al., Ann Neurol. 38: 943-50: 1995), proteolipid protein (Ibid), myelin-associated glycoprotein (Baig et al., Neurology 41: 581-7: 1991) and 2′,3′-cyclic nucleotide 3′-phosphodiesterase (Walsh and Murray, JCI 101: 1923-31: 1998) are present in multiple sclerosis patients but their role in disease pathogenesis is enigmatic and controversial.
A key autoimmune response in MS is targeted to certain regions of myelin basic protein. The major T and B cell response in the central nervous system of MS patients who are HLA DR2 (about two thirds of patients) is directed to a region between residues 84 and 103 of MBP (Steinman (1995) Nature 375:739-740; Warren et al. (1995) P.N.A.S. 92:11061-11065). The B cell response to MBP in MS has also been studied extensively. IgG purified from brain lesions reacted with the same region of MBP, p 85-96, that is the immunodominant T cell epitope in MS patients who are HLA DR2b (DRB1*1501) and overlaps with the T cell epitope in MS patients who are DR2a (DRB5*0101).
Relevant Literature
Copolymer-1 is a mixture of polypeptides composed of alanine, glutamic acid, lysine, and tyrosine in a molar ratio of approximately 6:2:5:1, respectively. It is synthesized by chemically polymerizing the four amino acids forming products with average molecular weights of 23,000 daltons (U.S. Pat. No. 3,849,550). Cop 1 binds promiscuously, with high affinity and in a peptide-specific manner to purified MS-associated HLA-DR2 (DRB1*1501) and rheumatoid arthritis-associated HLA-DR1 (DRB1*0101) or HLA-DR4 (DRB1*0401) molecules (Fridkis-Hareli et al. (1999) J Immunol 162(8):4697-704). Protruding N-terminal ends of Cop 1 bound to HLA-DR1, -DR2, or -DR4 molecules were then treated with aminopeptidase I, followed by elution, HPLC, and pool sequencing. In contrast to untreated or unbound Cop 1, this material exhibited distinct motifs at some positions with increases in levels of E at the first and second cycles, of K at the second and third cycles, and of Y (presumably at P1 of the bound peptide) at the third to fifth cycles, regardless of the HLA-DR molecule employed. No preference was seen at the following cycles that were mainly A.
Cop-1 has been recently approved as a treatment for relapsing multiple sclerosis (MS). Evidence demonstrates that Cop-1 induces active suppression of CNS-inflammatory disease in animal models (Aharoni et al. (1997) P.N.A.S. 94(20):10821-6). In humans, Copaxone treatment was found to lead to a significant reduction in the mean annual relapse rate and stabilization of disability. The treatment was accompanied by an elevation of serum IL-10 levels, suppression of the pro-inflammatory cytokine TNF alpha mRNA, and an elevation of the anti-inflammatory cytokines TGF-beta and IL-4 mRNAs in PBLs (Miller et al. (1998) J Neuroimmunol 92(1-2):113-21).
Treatment of murine experimental autoimmune encephalomyelitis with a myelin basic protein peptide analog is described by Reiseter et al. (1998) J Neuroimmunol 91(1-2):156-70. A single administration of the MBP peptide analog, Ac1-11[4Y], reduced disease severity, accompanied by a dramatic and selective loss of neutrophil pleiocytosis. A longer course of peptide therapy resulted in complete recovery from clinical signs of disease, and decreased pleiocytosis by all cell types. Wraith et al. (1989) Cell 59:247-255 describe antigen recognition in autoimmune encephalomyelitis and the potential for peptide mediated immunotherapy. Sakai et al. (1989) Proceedings of the National Academy of Sciences USA 86:9470-9474 describe the prevention of experimental encephalomyelitis with peptides that block interaction of T cells with major histocompatibility complex proteins. Karin. et al. (1994) J.E.M. 180:2227-2237 demonstrate the reversal of experimental autoimmune encephalomyelitis by a soluble variant of a myelin basic protein epitope.
It has been reported that administration of myelin basic protein can lead to immune tolerance (see, for example, Steinman et al. (1977) Nature 265:173; Tonegawa (1997) J Exp Med 186(4):507-15; Hafler et al. (1997) Ann N Y Acad Sci 835:120-31; Kennedy et al. (1997) J Immunol 159(2):1036-44). Various forms of Ag-specific tolerance have been demonstrated, included the administration of peptide coupled splenocytes, i.p. administration in incomplete adjuvant, oral and nasal administration.